A mechanically ventilated underground tunnel complex that lies 40m beneath the Upper Barrakka Gardens, this housed Britain's top-secret command in Malta during WWII and remained in use until 1977. Lovingly restored in 2009, the rooms are laid out as they would have been, staffed by waxwork figures, and provide a fascinating behind-the-scenes glimpse. Get here by going to the Saluting Battery in the Upper Barrakka Gardens – the staff there will direct you.
At the time of writing, there were plans to also restore and open the adjacent Combined Operations Centre, Malta's WWII nerve centre where the unified offensive response for all naval, air force and military action was coordinated. Check the Wirtartna website (www.wirtartna.org) for updates.